Industrial two phase reactions, such as hydrogenation reactions, are often performed by using finely divided powdered slurry catalysts in stirred-tank reactors. These slurry phase reaction systems are inherently problematic in chemical process safety, operability and productivity. The finely divided, powdered catalysts are often pyrophoric and require extensive operator handling during reactor charging and filtration. By the nature of their heat cycles for start-up and shutdown, slurry systems promote co-product formation which can shorten catalyst life and lower yield to the desired product.
An option to the use of finely divided powder catalysts in stirred reactors is the use of fixed bed reactors, e.g., pelleted and particulate catalysts or monolith catalysts. While this reactor technology does eliminate much of the handling and waste problems associated with stirred tank reactors, there are a number of engineering challenges. E.g., inadequate mixing and inadequate heat transfer have not permitted the general application of fixed bed reactor technology to reactions involving many organic compounds. On the other hand, stirred tanks provide for excellent mixing assuring homogeneity of reactants and they provide for excellent heat transfer. It is highly desirable to attain the benefits of fixed bed catalysts and stirred tank reactors to be combined in a practical reactor system.
The following articles and patents are representative of catalytic processes employing monolith catalysts and processes in two-phase chemical reactions including the hydrogenation of nitroaromatics and other organic compounds.
Hatziantoniou, et al. in “Mass Transfer and Selectivity in Liquid-Phase Hydrogenation of Nitro Compounds in a Monolithic Catalyst Reactor with Segmented Gas-Liquid Flow”, Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 4, 964–970 (1986) discloses the isothermal hydrogenation of nitrobenzene and m-nitrotoluene dissolved in ethanol using a monolithic catalyst impregnated with palladium. The authors report that the activity of the catalyst is high and therefore mass-transfer is rate determining. Hydrogenation was carried out at 590 and 980 kPa at temperatures of 73 and 103° C. Again, less than 10% conversion per pass was achieved. Ethanol was used as a co-solvent to maintain one homogeneous phase.
U.S. Pat. No. 4,743,577 discloses metallic catalysts which are extended as thin surface layers upon a porous, sintered metal substrate for use in hydrogenation and decarbonylation reactions. In forming a monolith, a first active catalytic material, such as palladium, is extended as a thin metallic layer upon a surface of a second metal present in the form of porous, sintered substrate. The resulting catalyst is used for hydrogenation, deoxygenation and other chemical reactions. The monolithic metal catalyst incorporates catalytic materials, such as, palladium, nickel and rhodium, as well as platinum, copper, ruthenium, cobalt and mixtures. Support metals include titanium, zirconium, tungsten, chromium, nickel and alloys.
WO 98/30323 discloses a process for carrying out a reaction between a reactant gas and reactant liquid in the presence of a monolith catalyst. In operation, a reactor is filled with reactant liquid and the monolith catalyst is rotated about a horizontal shaft, alternately in the liquid phase and then in the gas phase.
In an article entitled ROTACAT: A Rotating Device Containing a Designed Catalyst for Highly Selective Hydroformylation, Adv. Synth. Catal. 2001, 343, 201–206 there is disclosed a 200 mL autoclave which is charged with two parallel monolith cylindrical tubes which are rotated about a vertical axis. Reaction is effected while the monolith catalytic reactor is rotated within the liquid medium.